1. Field of the Invention
The present invention relates to a solid-state image pick-up device in which a photoelectric converting layer for generating a signal charge corresponding to a quantity of an incident light is laminated on a semiconductor substrate on which a signal reading circuit is formed, and more particularly to a photoelectric converting layer lamination type solid-state image pick-up device in which S/N of an image signal obtained by a photoelectric converting layer is enhanced.
2. Description of the Related Art
A prototype unit of a photoelectric converting layer lamination type solid-state image pick-up device has been described in JP-A-58-103165, for example. The solid-state image pick-up device has a structure that three photosensitive layers are laminated on a semiconductor substrate and respective electric signals for red (R), green (G) and blue (B) colors detected by each photosensitive layer are read by an MOS circuit formed on a surface of the semiconductor substrate.
The solid-state image pick-up device having such a structure was proposed in the past. Subsequently, a CCD type image sensor and a CMOS type image sensor in which a large number of light receiving portions (photodiodes) are integrated on a surface portion of the semiconductor substrate and color filters for red (R), green (G) and blue (B) colors are laminated on each light receiving portion have progressed remarkably. At present, an image sensor in which several million light receiving portions (pixels) are integrated on a chip is mounted on a digital still camera.
However, the techniques of the CCD type image sensor and the CMOS type image sensor have progressed to an almost limit and a size of an opening of one light receiving portion has been close to a wavelength order of an incident light, that is, approximately 2 μm. For this reason, they have been confronted with a problem in that a manufacturing yield is poor.
Moreover, an upper limit of a quantity of optical charges stored in one light receiving portion which is microfabricated is small, that is, approximately 3000 electrons. Consequently, it has also been difficult to finely represent 256 gradations. For this reason, it has been hard to expect a more excellent image sensor of a CCD type or a CMOS type in respect of picture quality or a sensitivity.
As a solid-state image pick-up device for solving these problems, a solid-state image pick-up device proposed in JP-A-58-103165 has been reconsidered. Consequently, image sensors described in Japanese Patent No. 3405099 and JP-A-2002-83946 have been proposed newly.
The image sensor described in Japanese Patent No. 3405099 has such a structure that hyperfine particles of silicon are dispersed in a medium to form a photoelectric converting layer and three photoelectric converting layers having sizes of the hyperfine particles changed are laminated on a semiconductor substrate, and electric signals corresponding to quantities of received lights for red, green and blue colors are generated from each of the photoelectric converting layers.
Also in the image sensor described in JP-A-2002-83946, three nanosilicon layers having different particle sizes are laminated on a semiconductor substrate and each of electric signals for red, green and blue colors which are detected in the respective nanosilicon layers is read onto a storage diode formed in a surface portion of the semiconductor substrate.
FIG. 5 is a typical sectional view corresponding to two pixels for the related-art photoelectric converting layer lamination type solid-state image pick-up device. In FIG. 5, a high concentration impurity region 2 for storing a red signal, an MOS circuit 3 for reading a read signal, a high concentration impurity region 4 for storing a green signal, an MOS circuit 5 for reading a green signal, a high concentration impurity region 6 for storing a blue signal and an MOS circuit 7 for reading a blue signal are formed on a surface portion of a P well layer 1 provided on an n-type silicon substrate.
Each of the MOS circuits 3, 5 and 7 is constituted by impurity regions for a source and a drain which are formed on the surface of the semiconductor substrate and a gate electrode formed through a gate insulating layer 8. An insulating layer 9 is laminated on the gate insulating layer 8 and the gate electrodes and is flattened and a shielding layer 10 is laminated thereon. In many cases, the shielding layer is formed by a thin metal layer. Therefore, an insulating layer 11 is further formed thereon.
Signal charges stored in the high concentration impurity regions 2, 4 and 6 for storing the color signals are read to an outside by the MOS circuits 3, 5 and 7.
A pixel electrode layer 12 divided for each pixel is formed on the insulating layer 11 shown in FIG. 5. The pixel electrode layer 12 for each pixel is conducted through a columnar electrode 13 to the high concentration impurity region 2 for storing a red signal for each pixel. The columnar electrode 13 is electrically insulated from components other than the pixel electrode layer 12 and the high concentration impurity region 2.
A photoelectric converting layer 14 for detecting a red color is laminated on the pixel electrode layer 12 in a one-sheet structure in common to each pixel, and furthermore, a transparent common electrode layer 15 is formed thereon in a one-sheet structure in common to each pixel.
Similarly, a transparent insulating layer 16 is formed on the common electrode layer 15 and a transparent pixel electrode layer 17 divided for each pixel is formed thereon. Each pixel electrode layer 17 and the high concentration impurity region 4 for storing a green signal for each pixel corresponding thereto are conducted through a columnar electrode 18. The columnar electrode 18 is electrically insulated from components other than the pixel electrode layer 17 and the high concentration impurity region 4. A photoelectric converting layer 19 for detecting a green signal is formed on each pixel electrode layer 17 in a one-sheet structure in the same manner as the photoelectric converting layer 14, and a transparent common electrode layer 20 is formed thereon.
A transparent insulating layer 21 is formed on the common electrode layer 20 and a pixel electrode layer 22 divided for each pixel is formed thereon. The pixel electrode layer 22 is conducted to the high concentration impurity region 6 for storing a blue signal for each pixel corresponding thereto through a columnar electrode 26. The columnar electrode 26 is electrically insulated from components other than the pixel electrode layer 22 and the high concentration impurity region 6. A photoelectric converting layer 23 for detecting a blue signal is laminated on the pixel electrode layer 22 in a one-sheet structure in common to each pixel, a transparent common electrode layer 24 is formed thereon and a transparent protective layer 25 is formed as an uppermost layer.
When a light is incident on the solid-state image pick-up device, optical charges corresponding to the quantities of incident lights having blue, green and red colors are excided in each of the photoelectric converting layers 23, 19 and 14. A voltage is applied between the common electrode layers 24, 20 and 15 and the pixel electrode layers 22, 17 and 12 so that the respective optical charges flow into the high concentration impurity regions 2, 4 and 6 and are read as blue, green and red signals to an outside through the MOS circuits 3, 5 and 7.
In the related-art photoelectric converting layer lamination type solid-state image pick-up device shown in FIG. 5, there is a problem in that a difference in a sensitivity for each color is made and a color balance of a pick-up image is thus lost to cause a deterioration in picture quality if the photoelectric converting efficiencies of the photoelectric converting layers 14, 19 and 23 are not equal to each other. Moreover, there is also a problem in that S/N is reduced because of an insufficient pixel separation of a detection signal through each pixel electrode layer. Furthermore, there is also a problem in that a quantity of a received light in a peripheral part of the solid-state image pick-up device is smaller than that in a central part thereof and shading is thus generated in an incorporation in a digital still camera in some cases.